FOS- and sugar-free inulin may be the missing ingredient. It feeds beneficial probiotics without feeding bad bacteria.
Many of my candida clients use this to avoid the high cost of probiotics, and believe me, I have the experience. The probiotic companies don't tell you this but if you feed the beneficial beasts they can fluorish and outcompete candida and bad bacteria.
In an nutshell, FOS and native inulin can be useful, but mainly to people without much of a problem. Both contain some Sugar and FOS, both of which can be problematic to existing infections. So we use instead a much more specific prebiotic that feeds bifidobacteria strains and to a certain extent, lactobacilli strains, but not the bad bacteria and yeasts.